Everyone WILL be copying the iPhone UI, but it will take them a long time to do so.
i would guess u are talking about OS UI, not hardware UI? since apparent LG's stuff has similar hardware UI, i.e. looks of the machine.
about OS UI, i don't know, just like u said, it take long time to develop an OS to compete with iphone, and the players in the market (smartphone market, palm, RIM, Samsung, etc, etc,) now all have their own OSs, before the real outcome of iphone's market future, i think of no reason for them to rush to mimic iphone's OS UI.
finally, for mac and pc, ur comparison has a point, OSX's UI looks much nicer than windows. But im not sure if u can say the same thing for smartphones, palm OS, windows Mobile, RIM's blackberry, and LG's new gadget, for such a small screen, how important is the nice OS UI? or is iphone's UI nice enough when compare to other smartphones?
I kinda feel there are a whole lot more thing ppl will consider before they think about UI when they are in the market for a smartphone.